How to dispose a class in .net?

The .NET garbage collector will eventually free up memory, but what if you want that memory back immediately? What code do you need to use in a class MyClass to call

MyClass.Dispose()
and free up …

Disposing needed in Unity?

Probably a Unity beginner’s question: when using Unity, would you still need to implement Dispose methods on the objects you have injected? Or is even this not needed (so, done automatically by Unity)?…